Such powered hammers can be employed to conduct demolition works wherein a tool bit formed as a chisel is usually driven into the material of the work piece. In addition, it can be conceived that the hammer is constructed as a hammer drill with a tool holder which is also rotationally driven. In this case a drill bit may be used as tool bit rather than a chisel.
In both cases considerable vibrations occur during use which are due to the percussion mechanism. These vibrations are transferred to the user via a handle mounted on the hammer housing and due to the high performance of chisel or demolition hammers the problem arises that the vibrations can reach a considerable strength and may cause damage to the user's health. Thus it is required to provide for an effective dampening mechanism.
From the prior art it is known to employ passive dampening systems in a powered hammer. For this purpose the handle can be decoupled from the main housing so as to reduce the amplitude of the vibrations transferred to the handle.
Furthermore, EP 1 252 976 A1 discloses a hammer with a dampening mass within the hammer housing which mass is movable in the moving direction of the ram and, thus, in the longitudinal direction wherein the mass is supported by two springs. The system comprising the mass and the springs is dimensioned in such a manner that the resonance frequency of the system corresponds to the frequency with which the ram impinges on the tool bit and the beat piece, respectively. During use the mass is stimulated to oscillate opposite to the reciprocating movement of the ram, and hence the overall vibrations of the hammer are reduced.
In addition, there are active dampening systems known from the prior art which systems employ a counter mass which is directly driven by the percussion mechanism wherein the counter mass is moving in an opposite direction relative to the ram.
However, the prior art dampening systems do not allow to control the amplitude and the time dependence of the movement of the dampening mass. In particular it is not possible to control the effect of the dampening system depending on the vibrations which are present on the housing of the hammer.
Moreover, the regulations regarding the maximum amplitude of vibrations occurring on hammers have recently been considerably tightened which results in a further need for a better vibration reduction on these tools.
Therefore, it is the object of the present invention to provide a powered hammer wherein the vibrations generated by a the hammer and transferred to a user are effectively reduced.